Transponders may be used in a variety of applications such as positioning and navigation, e.g. for avalanche rescue and fire rescue missions.
Heliskiing, for example, is a sport in which a helicopter is used to carry skiers to slopes outside the normal ski areas in order for them to ski in deep powder. However, there is a potential risk that skiers are lost and injured during off-piste skiing near trees since voids underneath the snow surface may be formed which are not visible from above.
Today, during avalanche rescue missions, a detector unit is used to detect missing persons that carry passive transponders. The most commonly used type of avalanche rescue equipment is that produced by the Swedish company “RECCO AB”. However, the passive transponders have a limited range. A description of a prior art passive harmonic transponder may be found in U.S. Pat. No. 6,456,228 by Granhed at el. The definition of a passive transponder is that a signal is transmitted from the transponder when hit by an incoming signal without any energy source involved.
In an alternative solution, the skiers are provided with an active transponder having an energy source that is used for transmitting a signal, when hit by an incoming signal, to enable an increase of the range of detection.
A different type of solution has been evaluated in a White Paper on Firefighter Location Systems by MSA, ID 0107-21-MC/January 2008, using a 2.4 GHz RF transmitter to locate people during a rescue operation. A fundamental drawback with this system is that the rescue personnel need to avoid detection of reflected signals within a building when trying to find a victim. Rescue personnel may even be lead in the opposite direction of the victim.
Thus there is a need for a new type of transponder.